Why do I have to turn off TV1 (even if the hdmi cord is unplugged) to change channels on TV2?

My parents have an older Dish Network system, it's not a Hopper or Joey or anything remotely fancy. It's just a basic Dish system with a DVR that's approximately 7 or 8 years old. They are having a weird issue where they can't change channels, or use the TV2 remote unless TV1 is completely unplugged. Just as a test I completely disconnected HDMI cords and all audio/video connections to other devices coming from the Dish receiver and still the same result. Now their TV2 has a coaxial cable ran to it, then it has a small antenna to act as a remote receiver on that TV. This is an issue that they have had pretty much since they got this particular receiver, even the installer had a hard time getting it to work when it was put in. Does anyone have a solution besides turning off the TV? If I need to share any photos or videos of anything to help shed light on this situation, I can definitely do so. Thank you redditors.